CODEWITHSUNDEEP
c#.nettask-parallel-library
Hari Subramaniam
Hari Subramaniam

Reputation: 1876

Task parallel library - Parallelism on single core

I am working on a WPF application.
In a screen/View i have to make 6 calls to a WCF service. None of those calls are related in the sense they dont share data neither are they dependent on each other. I am planning to use TPL and make these 6 WCF service calls as 6 tasks. Now the application might be either deployed on a single core machine or multiple core machine.

I am being told that usage of TPL on single core machine would actually increase the time take for the tasks to complete because of the overhead that would be placed on the cpu scheduler to time splice different tasks. Is this true. If yes should i still continue with my design or should i look at alternatives.

if i have to look at alternatives, what are those alternatives :) ?

Upvotes: 2

Views: 2660

Answers (3)

Phreon
Phreon

Reputation: 51

Your best bet is to profile using multi-core and single core. Most bios's can set the number of active core's so it shouldn't be a big problem. You can do some mock testing to find out if it will work for you.

Obviously using task switching has overhead issues but as long as each task's time is much longer than the setup time you won't notice it.

There are many ways to implement multi-tasking behavior and if you do not know which is best then chances are you need to actually write some test cases and do some profiling. This is not difficult to do. If you are simply trying to use multi-core systems then it generally is quite easy with the latest version of .NET and you can even set it up for multi-core but revert back to single core by using appropriate constructs.

the async/await pattern, for example, can easily be ran synchronously by either using #ifdef or removing all await keywords(with a search and replace tool). Parallel.For loops are easily convertible to normal for loops either directly or by changing MaxDegreeOfParallelism. Tasks can easily be ran synchronously.

If you would like to make it more transparent you could use some pre-processing scripting like T4.

Upvotes: 3

Dor Cohen
Dor Cohen

Reputation: 17080

In general, When running multi threads on single core it will be slower since it has Context Switch between the threads.

I think the following diagram will explain you the difference:

Context Switch

As you can see the diagram refer to 4 threads running on single core, first time in multi-tasking and the second time Sequential.

you can see that in multi-tasking all threads will finish at a later time than Sequential tasking.

In your specific case in probably won't be the same and I think @Guffa is right in his answer since its involving WCF calling

Upvotes: 2

Guffa
Guffa

Reputation: 700242

When doing something CPU intensive, you would be adding overhead by running parallel threads on a single core machine.

In your case the tasks are not CPU intensive, they are waiting for a service call to respond, so you can very well run parallel threads on a single core machine.

Depending on how the server handles the calls, there might not be any time increase anyway. If the calls are queued on the server, it will take about the same time to run all calls anyway. In that case it would be better to run the calls in sequence, just because it's simpler.

Upvotes: 5

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